Astronomy Picture of the Day
September 28, 2014

Transverse Aeolian Ridges
Transverse Aeolian Ridges

Credits: NASA/JPL/University of Arizona - Credits for the additional process. and color.: Dr Paolo C. Fienga/LXTT/IPF

The Tropics of Mars are commonly littered with small and (relatively) bright Ripples that were somehow shaped, in time, by the Dominant Winds blowing over the Region where they were found. The Ripples that we can see here, commonly called "Transverse Aeolian Ridges", or TARs, are Sandy (and/or Dusty) Surface Features which stand up to 6 meters (such as about 19,68 feet) tall and are spaced a few tens of meters apart. What makes them particular is the fact that they are typically oriented transversely as to the modern days' Dominant Wind Direction, as well as that they often found on the Floors of both Channels (and Fissures) and Impact Craters. The physical process that produces these Features is still unknown; however, most TARs display no evidence of Internal Structure, so it is difficult to discern exactly how they were formed.

While validating a HiRISE Digital Terrain Model of this area, Sarah Mattson, of the University of Arizona, discovered these rare "Banded TARs" in Iapygia, South of Syrtis Major. These Features, in fact, resemble TARs that were found elsewhere on Mars, except that the ones visible in this picture show Bands (or Layers) on their North/Western Faces, but fewer - or even none - on their South/Eastern sides.

One possible interpretation of this strange Layering is that these particular TARs are made up of Wedge-shaped Layers and, if this hypothesis were correct, it could reasonably be implied that the Ripples grew vertically over time, as some Sandy and Dusty Material accreted at the Crests of the Ridges. Furthermore, it also suggests that the Banded Slopes, while this process took place, were faced Upwind. This observation might provide a valuable clue to the formation of TARs located elsewhere on Mars, if they have a similar Internal Structure but, unfortunately, that Structure cannot be seen yet, because the TARs are made up of homogeneous Materials which are substantially uniform in color.

Mars Local Time: 15:39 (Middle Afternoon)
Coord. (centered): 18,707° South Lat. and 62,601° East Long.
Spacecraft altitude: 259,1 Km (such as about 160,901 miles)
Original image scale range: 25,9 cm/pixel (with 1 x 1 binningso objects ~ 78 cm across are resolved
Map projected scale: 25 cm/pixel
Emission Angle: 2,5°
Phase Angle: 55,5°
Solar Incidence Angle: 53° (meaning that the Sun was about 37° above the Local Horizon at the time the picture was taken)
Solar Longitude: 209,4° (Northern Fall - Southern Spring)
Credits: NASA/JPL/University of Arizona
Additional process. and coloring: Lunar Explorer Italia

This picture (which is a NASA - Original Mars Reconnaissance Orbiter False Colors and NON Map-Projected sub-frame identified by the serial n. ESP_020782_1610-1) has been additionally processed, magnified to aid the visibility of the details, contrast enhanced, Gamma corrected, and then re-colorized in Absolute Natural Colors (such as the colors that a human eye would actually perceive if someone were onboard the NASA - Mars Reconnaissance Orbiter and then looked down, towards the Surface of Mars), by using an original technique created - and, in time, dramatically improved - by the Lunar Explorer Italia Team.

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